Friends of Brooke Mueller expressed extreme concern when the mother of twins completely fell off the radar last week -- she dumped the kids with her mother and stopped returning calls after begging pals for urine samples. She was later seen at a seedy pawn shop trying to sell an expensive men's watch -- possibly something from Charlie's personal collection -- and a stereo, despite the huge settlement and child support check she receives from the actor.

The kicker came when Mueller refused to submit to a court-ordered random drug test on Friday. According to her child custody settlement agreement with Sheen, both parties are required to submit to random testing, and any refusal counts as a dirty test.

What does this mean? Charlie Sheen has a great chance of getting back custody of the twins. Despite the actor's ranting, raving, weirdly stream-of-consciousness semi-successful stage shows and delusional thoughts of getting back on Two and a Half Men, by all accounts he actually has been clean and sober since his rehab-at-home.

In what appears to be a pre-emptive strike, Mueller entered rehab for the dozenth time or so over the weekend -- but it may be too little, too late. Sheen's lawyer will be asking a judge to make Brooke hand the kids over to him full time while she's back in treatment.

"Charlie has had enough with her excuses, period," said a Sheen source. "Brooke refused to take a random drug test. Charlie's attorney will use that as evidence that the boys are better off with him than with Brooke."

Keep reading SheKnows for more updates as the Charlie Sheen custody battle brews!